The present inventor is also the inventor of the manhole casting positioning apparatus disclosed in U.S. Pat. No. 4,666,333 issued May 19, 1987. Manholes for sewers and the like are typically assembled by stacking a number of precast, cylindrical concrete barrel sections to approximately the desired height. In order to allow some adjustability of the placement of the iron manhole casting on the end of the manhole in relation to the road grade, a 1-inch to 20-inch space is typically left between the manhole lid and the iron casting. Previously this space was filled with layers of bricks, which is expensive and time consuming. The apparatus disclosed in U.S. Pat. No. 4,666,333 provides a two-piece form, consisting of an inner and outer sleeve, which replaces the brick and mortar method.
In the inventor's apparatus disclosed in U.S. Pat. No. 4,666,333, the inner sleeve consists of a single planar plastic piece joined end-to-end to form a cylinder which is expandable by means of turnbuckle-type expansion mechanisms. The outer sleeve is in the form of a belt with a receptacle at one end through which the other end passes and is secured to form a cylinder. The inner sleeve is first expanded into the manhole opening and set to the required slope. The casting is mounted on the inner sleeve, and the outer sleeve, which has a diameter greater than that of the base of the casting, is placed around the casting. Concrete is then poured between the inner and outer sleeves and up over the base of the casting. After the concrete has set the sleeves are removed.
The previous casting positioning apparatus incorporated a number of turnbuckles in connection with the inner sleeve (to tighten the sleeve against the manhole) which were time consuming to adjust and relatively expensive to manufacture. Also there was a possibility of leakage of water through the inner form of the prior device. A casting positioning apparatus which is simpler, more easily adjustable prior to pouring of the concrete, and provides a leak-proof inner surface is therefore desired.